Force India say they will persist with a new wheelnut system despite having to retire both their cars at Sunday's Malaysian Grand Prix because of problems with it in pitstops.

Britain's Paul Di Resta and Germany's Adrian Sutil both missed out on likely points at Sepang as mechanics struggled in vain to remove and replace wheels using a 'captive wheelnut' system.

"Both cars had the same problem with the wheel nuts and it cost us a lot of time in the pits," said Sutil. "We're not sure exactly what happened yet so the team stopped the cars to make sure we understand the issue."

The system was first used in the Australian season-opener without any trouble, but the temperatures in Malaysia were much higher.

"We won't go back to the old part," deputy team principal Bob Fernley told autosport.com. "We can't go backwards, you need to cure the problem and carry on with your development. Today, everyone's pitstops are well under four seconds but if you go back to the traditional route you are plus four."